Effects of ruminal infusion of volatile fatty acids on plasma concentration of growth hormone and insulin in sheep.

In an initial experiment we observed postprandial changes in plasma concentrations of growth hormone (GH), insulin, glucagon, and somatostatin (SRIF) in sheep. We then examined whether increasing the rumen concentration of volatile fatty acids (VFA) by infusing a VFA mixture at three rates (53.5, 107, and 214 micromol/kg/min for 4 hr) mimicked the postprandial changes in hormone secretion. Feeding significantly (P < 0.05) suppressed the plasma GH concentration for 6 hr, whereas it significantly (P < 0.05) increased plasma concentrations of insulin, glucagon, and SRIF. Plasma glucose levels tended to decrease after feeding but then gradually increased over the prefeeding level (P < 0.05). Intraruminal infusion of the VFA mixture at 107 micromol/kg/min caused similar changes in ruminal VFA concentrations to those seen after feeding. The infusion significantly (P < 0.05) suppressed GH secretion in a dose-dependent manner, whereas it caused a significant (P < 0.05) increase in insulin and glucose concentrations without changing glucagon concentrations. From these results, we conclude that the postprandial change in ruminal VFA concentration may be a physiological signal which modifies GH and insulin secretion in sheep.

Plasma glicentin in diabetic and gastrectomized patients.

Recent successful synthesis of human glicentin prompted us to establish an immunoassay method for determination of human glicentin in plasma. Human glicentin in plasma was measured using a newly developed sandwich ELISA. The mean fasting levels of human glicentin were 18.6+/-2.4 and 19.7+/-2.1 pM in normal subjects and diabetic patients, respectively. In diabetic patients with renal failure, plasma glicentin was elevated, exceeding 100 pM. In normal subjects, plasma glicentin increased to a peak level of about 130 pM at 60 min after an oral glucose load, and then decreased. In patients who underwent gastrectomy, plasma glicentin rapidly increased to a peak of about 300 pM at 30 min after oral glucose load. In a patient with short bowel syndrome plasma glicentin did not change following an oral glucose load. These results correspond with previous findings for gut glucagon-like immunoreactive materials (GLI) or enteroglucagon. We conclude that glicentin is secreted from the small intestine in response to intraluminal glucose stimulation in humans.

Inhibition of GH releasing factor (GRF)-induced GH secretion by intraruminal infusion of volatile fatty acids (VFA) in sheep.

A VFA mixture solution containing acetate, propionate and butyrate (the molar ratio of acetate, propionate and n-butyrate = 61.7:24.3:14.0) was infused into the rumen at various rates (53.5, 107 and 214 mumol kg-1 min-1) over 6 h to examine the effects on basal and growth hormone-releasing factor (GRF, 0.25 micrograms kg-1)-induced increase in secretion of GH, insulin, glucagon and somatostatin (SRIF) in five castrated male sheep. Intraruminal infusion of the VFA mixture into the 18-h-fasted animals at the rates of 53.5, 107 and 214 mumol kg-1 min-1 finally raised the total intraruminal VFA concentration from 91.4 to 100.2 (P > 0.05), 175.9 (P < 0.05) and 234.5 (P < 0.05) mmol l-1, respectively. A preliminary experiment showed that an infusion rate of 107 mumol kg-1 min-1 mimics the postprandial increase in ruminal VFA. The basal plasma GH concentrations (2 to 4 h after the start of VFA infusion) and the area under the profiles for GH release in response to the intravenous GRF injection, which was done 4 h after the start of VFA infusion, were significantly decreased by the VFA infusion rates of 107 and 214 mumol kg-1 min-1. Furthermore, the VFA infusion noticeably increased basal plasma concentrations of insulin, but it scarcely changed the basal levels of glucagon, SRIF and glucose. From these results we conclude that an increase in the ruminal VFA concentration, even within the physiological range, would suppress GH secretion from the ovine anterior pituitary, and that the postprandial rise in the ruminal VFA concentration may be one of the factors normally suppressing GH secretion in sheep.

Insulin and glucagon secretion in goats (Capra hircus Linnaeus) exposed to cold.

Cold exposure significantly decreased the insulin response to the intravenous injection of arginine, butyrate and tolbutamide, and tended to reduce the response to glucose in goats. The glucagon responses to these test materials were not different between warm and cold environments. Intravenous phentolamine infusion tended to increase, and propranolol infusion decreased insulin secretion more effectively in the cold than in the warm environment. It is concluded that cold exposure decreases insulin secretion in response to a variety of stimuli in goats.

Insulinotropic action of human glicentin in dogs.

Glicentin has been demonstrated to be released in response to the intraluminal administration of nutrients, but its biological action remains unknown. To clarify the effect of glicentin on the endocrine function of the pancreas, the present study was performed using an in vivo local circulation system of the canine pancreas. During infusion of 0.5% solution of glucose or arginine, 100 and 400 pmol glicentin and 400 pmol glucagon were administered into the pancreaticoduodenal artery (PA) within 10 minutes at 40-minute intervals successively. During glucose infusion, blood glucose in the femoral artery did not change following administration of 100 pmol glicentin, but slightly increased following 400 pmol glicentin. Plasma insulin (immunoreactive insulin [IRI]) in the pancreaticoduodenal vein (PV) increased significantly only following infusion of 400 pmol glicentin. Plasma glucagon (immunoreactive glucagon [IRG]), measured with a specific antiserum to the C-terminal portion of glucagon, did not change following administration of 100 pmol glicentin, but was slightly elevated following 400 pmol glicentin. Plasma total IRG, measured with a nonspecific antiserum, increased promptly after administration of 100 and 400 pmol glicentin. During arginine infusion, the response of plasma IRI to glicentin was markedly exaggerated both in dosages of 100 and 400 pmol. From the present study it was concluded that human glicentin clearly increases insulin release from the canine pancreas.

Effect of C-terminal fragments of glucagon on insulin secretion in dogs.

Although the insulinotropic action of glucagon is well known, which parts of the glucagon molecule play an important role in its action remain to be elucidated. To investigate the direct effect of the C-terminal peptides of glucagon on the endocrine function of the pancreas, glucagon (17-29), (21-29), (23-29), and (25-29) were studied using an in situ local circulation system of the canine pancreas. These glucagon fragments, as well as glucagon(1-29), were infused into the superior pancreaticoduodenal artery (PA) in a dosage of 400 pmol for 10 minutes during 0.5% glucose or 0.5% arginine infusion, and plasma insulin (IRI) and glucagon (IRG) levels in the superior pancreaticoduodenal vein (PV) were determined. During the glucose infusion, plasma IRI increased significantly following the administration of glucagon(23-29), (21-29), (17-29), or (1-29), but not glucagon(25-29). In these experiments, plasma IRG increased significantly following infusion of glucagon(21-29), (17-29), or (1-29). During the arginine infusion, all of the glucagon fragments studied enhanced insulin secretion, whereas plasma IRG was increased following the administration of glucagon(21-29), or (1-29). In these experiments with glucose or arginine infusion, blood glucose in the femoral artery (FA) did not change significantly except for glucagon(1-29), which increased the blood glucose level. In addition, the administration of graded doses of glucagon(21-29) [50, 150, and 400 pmol] during the glucose infusion elicited an increase in plasma IRI in a dose-related manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effect of volatile fatty acids on GRF-induced GH secretion in sheep.

The effect of intravenous infusion of acetate, propionate and butyrate (0, 3, 10, 30 mumol kg-1 min-1 over 40 min) on the secretion of growth hormone (GH), insulin and glucagon in response to growth hormone-releasing factor (GRF) injection (0.25 micrograms/kg, 10 min after the onset of acid infusion) was determined in six sheep. The intravenous injection of GRF caused a marked increase in plasma GH at every dose of each acid. The GH response to GRF was unaffected by an intravenous infusion of acetate. The basal plasma levels of insulin, glucagon and glucose were unchanged by acetate infusion. The infusion of propionate markedly suppressed the GH response to GRF in a dose-dependent manner. Propionate produced increases in plasma insulin, glucagon and glucose concentrations. Butyrate infusion also caused a significant attenuation of GRF-induced GH secretion. Butyrate infusion stimulated the secretion of both insulin and glucagon and caused hyperglycemia. After cessation of the infusion of propionate or butyrate plasma GH tended to increase again. Plasma somatostatin concentrations, which were measured only for the highest dose of butyrate, were unchanged during acid infusion, but increased on discontinuing the infusion. It is concluded that propionate and butyrate suppress GH secretion, while stimulating the secretion of insulin and glucagon in sheep.

Mechanism of insulin secretion by midaglizole.

Midaglizole was introduced as a hypoglycemic agent, but its insulin releasing mechanism remains unknown. In the present study, the effect of midaglizole upon the B cell function of the pancreas was investigated, using an in situ local circulation of the canine pancreas. The graded doses of midaglizole (0.2, 1.0 and 2.0 mg/kg) revealed a dose-related response of plasma insulin. The administration of yohimbine, a classical alpha 2-antagonist (1.11 mg/kg) revealed a similar increase in plasma insulin to that with midaglizole of equimolar amount. During the clonidine infusion midaglizole did not elicit any significant rise in plasma insulin, whereas yohimbine increased plasma insulin significantly. During glucagon infusion plasma insulin increased following midaglizole infusion but not by yohimbine. The simultaneous administration of diazoxide (K-channel opener) suppressed the midaglizole-induced insulin secretion. These results obtained in the present experiments revealed a different mechanism of insulin releasing action of midaglizole from that of yohimbine. Furthermore, the finding with diazoxide administration suggests that midaglizole stimulates insulin release through an interaction of K(+)-channel of the pancreatic B-cell.

Insulin releasing action of N-terminal peptides of glucagon in dogs.

The relationship between the molecular structure and insulin releasing action of glucagon remains unknown. In order to investigate the direct action of N-terminal peptides of glucagon, glucagon (1-14), and glucagon (1-21) were studied using an in situ local circulation of the canine pancreas. These glucagon fragments as well as glucagon (1-29) were infused into the superior pancreaticoduodenal artery in a dose of 400 pmol for 10 min during the glucose or arginine infusion, and plasma insulin and glucagon in the superior pancreaticoduodenal vein were determined by radioimmunoassay. During the glucose infusion, glucagon (1-14) elicited a slight increase in plasma insulin, whereas glucagon (1-21) and (1-29) revealed significant changes in plasma insulin. In these experiments plasma glucagon did not change significantly following the administration of glucagon (1-14) or (1-21). During the arginine infusion all of the glucagon fragments studied enhanced insulin secretion markedly, whereas glucagon secretion was not affected. Furthermore, graded doses of glucagon (1-14) (50, 150, and 400 pmol) elicited an increase in plasma insulin in a dose-related manner. It is concluded from the present study that the N-terminal peptides of glucagon stimulate insulin release especially during the arginine infusion.

The structure-function relationship of GLP-1 related peptides in the endocrine function of the canine pancreas.

In order to clarify the relationship between the structure and function of glucagon-like peptide (GLP) 1 in the endocrine function of the pancreas, the response of insulin and glucagon to various synthetic GLP-1-related peptides was investigated in anesthetized dogs. GLP-1-related peptides were administered in a dosage of 400 pmol within 10 min into the pancreatic artery during glucose or arginine infusion and the changes in plasma insulin and glucagon in the pancreatic vein were studied. GLP-1 (7-36) and (7-37), as well as glucagon enhanced insulin release during glucose infusion, whereas neither GLP-1 (1-37), (7-20), (6-37) nor (8-37) stimulated insulin release. The administration of GLP-1 (1-37), (7-36) and (7-37) reduced glucagon release during glucose infusion. When arginine was infused, GLP-1 (7-20), (7-36), (7-37), and glucagon enhanced insulin release. In contrast, glucagon release was increased by the administration of GLP-1 (7-20), (8-37), and (7-37). The present study indicates that histidine at the 7th position of GLP-1 is important in eliciting biological action and that only truncated GLP-1 (7-36), (7-37), and (7-20) showed an insulinotropic action as strong as glucagon in dogs. Furthermore, it is suggested that the response of insulin and glucagon to GLP-1-related peptides is dependent on a background condition.

Alpha 2-adrenergic modulation of glucagon and insulin secretions in sheep.

To investigate the effects of alpha 2-adrenergic receptors on the secretions of pancreatic glucagon and insulin, clonidine, midaglizole and yohimbine were intravenously administered in four conscious sheep. Clonidine infusion at a dosage of 1.0 nmol/kg/min produced hyperglucagonemia, hypoinsulinemia and hyperglycemia. Midaglizole or yohimbine was infused for 30 min, at doses of 5, 10 and 50 nmol/kg/min during the clonidine infusion. The highest yohimbine infusion (50 nmol/kg/min) blocked the clonidine-induced responses of glucagon, insulin and glucose. On the other hand, the midaglizole (50 nmol/kg/min) infusion brought about no statistical effect on the clonidine-induced responses of glucagon, insulin and glucose. The alpha 2-adrenergic antagonistic effect of midaglizole was clearly less than that of yohimbine in the present experiments. It is concluded that the glucagon secretion is enhanced and the insulin release is inhibited by alpha 2-adrenergic stimulation in conscious sheep.

Effects of intravenous infusion of 17 amino acids on the secretion of GH, glucagon, and insulin in sheep.

The effects of intravenous infusion of 17 amino acids, each at a dose of 3 mmol/kg over 30 min, on the secretion of insulin, glucagon, and growth hormone (GH) were studied in 6 castrated male sheep. Insulin-like growth factor I (IGF-I) secretion was also studied using eight of the amino acids. Plasma alpha-amino nitrogen reached a peak at 30 min followed by a gradual decrease thereafter. The greatest increase was obtained using aspartic acid and the smallest with methionine, responses to the remaining amino acids lying between these two. Leucine was the most effective amino acid in stimulating insulin secretion but did not produce any increase in glucagon and GH secretion. Alanine, glycine, and serine induced a greater enhancement of both glucagon and insulin secretion than other amino acids. No amino acid was able to specifically stimulate glucagon secretion without also increasing insulin or GH secretion. With regard to insulin and glucagon secretion, amino acids could be divided into groups according to their R groups. Neutral straight-chain amino acids stimulated both insulin and glucagon secretion, with a greater secretory response to shorter C-chain amino acids. Branched-chain amino acids tended to enhance insulin and suppress glucagon secretion. Acidic amino acids caused an increase in GH secretion. Aspartic acid caused the strongest stimulation of GH secretion, exceeding that induced by arginine. No changes in plasma IGF-I were brought about by any of the amino acids tested.

Role of autonomic nervous system in the response of plasma pancreatic polypeptide to glycopenia in dogs.

The effect of cholinergic and adrenergic influences on pancreatic polypeptide (PP) release was studied in dogs. Administration of acetylcholine resulted in an elevation of plasma PP, whereas epinephrine induced no increase. Insulin-induced hypoglycemia increased plasma PP in a conscious state but not in anesthetized dogs. The infusion of phentolamine or propranolol did not affect the response of plasma PP to insulin-induced hypoglycemia, whereas atropine markedly inhibited the increase in plasma PP. Likewise, atropine reduced the rise of plasma PP during the intravenous administration of 2-deoxy-D-glucose (2-DG). We conclude from the present experiments that cholinergic mechanisms are of major importance in the response of PP to insulin- and 2-DG-induced glucoprivation, while the major role of the adrenergic mechanism was not proved.

Increased plasma glucagon-like immunoreactivity in dogs with ileojejunal transposition.

To elucidate hormonal and metabolic changes in intestinal adaptation, an experimental study was performed in dogs subjected to ileojejunal transposition. Fasting levels of blood glucose, plasma insulin and gastric inhibitory polypeptide (GIP) did not change significantly throughout 12 weeks. Plasma glucagon measured with an antiserum specific to the C-terminal portion of glucagon slightly increased and plasma total glucagon measured with a non-specific antiserum gradually increased. Glucose tolerance deteriorated at the 4th week in the transposed group. The response of plasma insulin and GIP to glucose in the transposed group did not differ from that of the sham operated group. Plasma glucagon increased significantly during glucose loading at the 12th week. The response of plasma total glucagon to glucose was most prominent, reaching a peak of 3,755 +/- 742 pmol/liter. The value was significantly increased, compared with that of the sham group or normal group (p less than 0.01). Insulin-induced hypoglycemia enhanced a larger increment of plasma total glucagon in the transposed group than in the sham group (p less than 0.05). At the 12th week plasma total amino acids were decreased and several amino acids were reduced. It is concluded that ileojejunal transposition elicited an exaggerated response of plasma total glucagon to glucose and several metabolic derangements and that the transposition offers an excellent model for hyperenteroglucagonemia.

Effect of a new lente insulin on diabetics.

Thirty diabetics who had been receiving ordinary insulin were switched to S-lente insulin, a new mixture of four parts semilente and six parts ultralente insulin. Eight times a day, we measured the glucose, insulin, and C-peptide (CPR) in their blood. Those with more than 250 mg/dl postprandial glucose were designated group A (18 patients) and the other were designated group B (12 patients). Group A diabetics experienced a significant decrease in fasting blood glucose levels whereas group B did not. S-lente improved the daily blood glucose profiles of 72% of group A and 25% of group B. It slightly reduced the sum of the daily blood glucose in group A and did not affect those of group B. The M-value fell significantly in group A but not in group B. Changes in this value correlated significantly with those of blood glucose determination sums. The sums of the determinations of free plasma insulin and CPR remained unaffected by the new insulin. It is concluded that S-lente insulin controls the blood glucose of diabetics whose postprandial blood glucose cannot be controlled by ordinary insulin.

Glucagon and insulin responses to alpha-adrenergic subtype receptor blockade in sheep.

1. Five sheep were used to investigate the influences of alpha-adrenergic subtype receptor blockade on the secretion of both glucagon and insulin. 2. The glucagon secretion was stimulated through an alpha 2-adrenergic subtype mechanism. 3. The secretion of insulin was inhibited by an alpha 2-adrenergic subtype mechanism in conscious sheep.

Effect of porcine pancreastatin on endocrine function of canine pancreas.

Controversial results concerning the modulation of insulin release with pancreastatin prompted us to investigate the effect of this peptide upon the endocrine function of the pancreas using an in situ perfusion method in dogs. Administration of porcine pancreastatin into the pancreaticoduodenal artery in a dosage of 0.34 micrograms/kg of body weight during arginine infusion increased slightly plasma insulin and lowered minimally plasma glucagon in the pancreaticoduodenal vein. Pancreastatin infusion in a dosage of 500 ng/min did not modify glucose-induced insulin release and glucagon suppression by glucose. Theophylline infusion induced a slight increase in plasma insulin and glucagon in the pancreaticoduodenal vein. Pancreastatin infusion accelerated slightly these changes in plasma insulin and glucagon following theophylline infusion. From the present experiment it is concluded that porcine pancreastatin did not inhibit glucose-induced insulin release from the canine pancreas, inconsistent with the first report on insulin release from the rat pancreas. Alternatively, porcine pancreastatin rather stimulated insulin release during arginine infusion or following theophylline administration.

Response of gut glucagon-like immunoreactivity to hypoglycemia in dogs.

Previous studies demonstrated that insulin-induced hypoglycemia enhances glicentin secretion in piglets and prompted us to investigate the response of glucagon-like immunoreactivity (GLI) to hypoglycemia in dogs. Insulin hypoglycemia did not induce any rise of plasma total immunoreactive glucagon (IRG) measured by nonspecific antiserum to glucagon in normal or pancreatectomized dogs under anesthesia. In contrast, insulin-induced hypoglycemia clearly increased plasma total IRG in both normal and pancreatectomized dogs in a conscious state. Administration of acetylcholine resulted in an elevation of plasma total IRG, whereas epinephrine induced a slight increase in plasma total IRG. The infusion of alpha- or beta-adrenergic blockers did not affect the response of plasma total IRG to hypoglycemia, whereas atropine completely blunted the increase in plasma total IRG during insulin hypoglycemia. Similarly atropine abolished the rise of plasma total IRG during intravenous administration of 2-deoxy-D-glucose. It is concluded that hypoglycemia clearly enhances the secretion of GLI from the gut in dogs and that GLI secretion during hypoglycemia is modulated, at least in part, by the autonomic nervous system.

Effect of intraluminal administration of amino acids upon plasma glicentin.

To see what effect intraluminal amino acids would have on glicentin secretion, we put a mixture of 10 amino acids (1 g/kg) into the duodenum of five normal, conscious piglets. Their plasma nitrogen rose, as did insulin and glucagon measured with C-terminal-specific antiserum. Plasma total immunoreactive glucagon, determined with non-specific antiserum, rose from 2753 +/- 460 pg/ml to a peak of 4434 +/- 1352 pg/ml at 30 min. Plasma glicentin, determined with R 64 antiserum, rose from a fasting level of 297 +/- 70 pmol/l to a peak of 702 +/- 167 pmol/l at 45 min. We also gave oral arginine to 6 pancreatectomized dogs to investigate why the plasma glicentin rises after amino acid ingestion. Arginine raised the plasma total immunoreactive glucagon from 1120 +/- 214 pg/ml to a peak of 2266 +/- 512 pg/ml at 45 min. We conclude that intraluminally administered amino acids enhance glicentin secretion from the gut.